Extraction of85Sr by a nitrobenzene solution of bis-1,2-dicarbollylcobaltate in the presence of 15-crown-5 (15C5, L) has been investigated. The equilibrium data and the typical maxima concerning the dependencies of the Sr distribution ratios on the analytical concentration of 15C5 in the system under study can be explained assuming that the HL+, HL2+ and SrL22+ species are extracted into the nitrobenzene phase. The values of the corresponding extraction and stability constants of the extracted species in nitrobenzene saturated with water have been determined.